The present invention relates to a loading device of a forklift truck and, particularly, to a loading device of a forklift truck, having a mast support shaft fixed to an outer mast by welding.
Japanese Patent Application Publication No. 2009-73618 discloses a mast device of a forklift truck. The mast device includes a pair of right and left outer masts that are connected with each other at positions adjacent to the top thereof by an upper stay that is disposed extending horizontally. A mast bracket having a shaft is welded to a rear wall of each outer mast. A lower beam is welded at the opposite ends thereof to the rear wall of the mast brackets. The lower beam enhances the rigidity of the mast device together with the upper stay and an intermediate stay. The shaft of the mast bracket is rotatably supported by the truck body at a front part thereof so that the mast device is pivotable back and forth on the shaft.
In the mast device of the above-disclosed structure and shown in FIG. 10, a mast support shaft 93 (corresponding to the shaft) is fixed by welding to a side plate 92 (corresponding to the mast bracket) that is fixed to an outer mast 91. The mast support shaft 93 includes a cylindrical shaft body 94 and a flange body portion 95 that is integrally formed with the shaft body 94. The flange body portion 95 is of a substantially cylindrical shape and coaxial with the axis of the shaft body 94. Numeral 96 designates a weld portion that is formed around the flange body portion 95 by welding to fix the mast support shaft 93 to the side plate 92. Since stress concentration occurs in the mast support shaft 93, the flange body portion 95 around which the weld portion 96 is formed needs to have a thickness that is large enough in the axial direction thereof to resist the stress concentration in the mast support shaft 93.
In the case that the mast support shaft is fixed on the outer side surface of the outer mast, however, the mast support shaft may be subject to design restrictions depending on dimensional conditions of the truck body and the outer mast that support the mast device. In such a case, the flange body cannot have enough thickness, so that the flange body cannot withstand the stress concentration in the weld portion between the mast support shaft and the outer mast.
The present invention which has been made in light of the problems mentioned above is directed to providing a loading device of a forklift truck which prevents stress concentration in the mast support shaft provided on the outer side surface of an outer mast.